The human eye possesses natural accommodation capability, which involves relaxation and constriction of the circular ciliary muscle of the eye, and zonules controlled by the ciliary muscle, by the brain to provide the eye with near and distant vision. This ciliary muscle action is automatic, and varies the shape of the natural crystalline lens to an appropriate optical configuration for focusing light rays entering the eye on the retina. Ciliary muscle relaxation, which is the normal state of the muscle, shapes the human crystalline lens for distant vision. Ciliary muscle contraction deforms the lens for near vision, and the extent of contraction changes the focal length of the lens to the desired endpoint. This change in effective focal length in order to focus on nearby objects is known as accommodation.
Normally the human eye loses its ability to accommodate as individuals reach the age of 40. This condition, known as presbyopia, is typically due to a progressive loss in the elasticity of the lens of the eye, such that the ciliary muscle can no longer exert the necessary deformation of the lens' shape. In addition, the human eye is susceptible to disorders and diseases which attack the crystalline lens, such as cataracts.
Cataracts causing partial or complete blindness are typically treated by removing the crystalline lens and replacing it with an intra-ocular lens (IOL). While conventional IOL's have had great success at restoring vision, they have limited ability for accommodation. The conventional solution to the problem of presbyopia is a prescription for reading glasses or, for individuals who already require glasses to correct other refractive errors such as myopia or astigmatism, a prescription of bifocal or multifocal glasses. This is necessary for the subject's eye to have clear vision of objects at different distances.
Alternative attempts in the art to overcome presbyopia focus on providing implantable IOL's with accommodation ability. Accommodative IOL's have been introduced, for example, which change the shape of the IOL by physically deforming the lens to become more convex for focusing on nearby objects, similar to the way the body's natural crystalline lens focuses. Other accommodative IOL's work by moving the IOL along its optical axis within the orbit of the eye. However, synthetic IOLs implanted in subjects for the treatment of cataracts typically do not have the ability to change shape as do natural lenses. Thus, subjects with synthetic accommodating IOL's still have presbyopia and cannot adequately focus on proximate visual targets due to the reduced flexibility of the IOL relative to the tractive capabilities of the ciliary muscle. Therefore, such subjects experience a degradation of their ability to accommodate.
It is believed that the neuromuscular activity of the ciliary muscle correlates with a person's effort to adjust the focus of the eye. Previously, enhancement of the physical movement of the ciliary muscle has been utilized for IOL accommodation. For example, U.S. Pat. No. 7,060,094 to Shahinpoor et al discloses a circularly distributed assembly of synthetic muscles in the form of mini-bridges for augmenting the contraction force of the ciliary muscle transmitted to the lens. However, it has been difficult to capture the action potential of the ciliary muscle and transfer it with enough force to cause IOL deformation, even when various multipliers such as micropumps or levers are used.
Other inventions aimed at improving the accommodative abilities of implantable IOLs include the following: U.S. Pat. No. 7,334,892 to Goodall et al discloses an adjustable lens system which detects a neural signal and then generates a control signal to drive actuation of an adjustable IOL.
U.S. Pat. No. 5,800,530 to Rizzo, III discloses an implantable and deformable IOL having microelectronic components implanted thereon, in which a micromotor controlled by a distance measuring apparatus changes tension in a band encircling the periphery of the lens to vary its focal length.
U.S. Pat. No. 5,203,788 to Wiley discloses micromotors powered by EMG or ultrasound to change the lens shape, in which each micromotor is responsive to an externally generated control signal for selectively changing the circumference and/or axial position of the lens. The changes made to the lens are not automatic and are not under the control of the subject.
U.S. Pat. No. 4,373,218 to Schacar discloses an expandable intra-ocular lens filled with liquid crystal material which could be activated by an electrical signal originated from the action potential of the ciliary muscle, sensed by an electrode which is sent to a microprocessor by miniature wiring.
While such prior art devices and methods for the surgical correction of presbyopia may be useful for their intended purposes, those developed to date have generally achieved limited success because they are unable to provide adequate accommodation when compared to a healthy natural crystalline lens, are too complex to be practical to construct, or fail to accurately and reliably focus on demand.
As such, it would be beneficial in the art to provide a system and method that provides an enhanced capacity for accommodation of implanted IOLs. It would also be beneficial to detect a signal, such as an action potential, created by the ciliary muscle and to convert this signal to activate micromotors and/or nanomotors implanted into the eye for creating accommodative forces. It would also be advantageous to mimic the force of contraction created by the ciliary muscle onto a native lens, thereby causing an accommodating shape change in an implanted IOL. It would also be advantageous to provide an IOL system that can detect and capture the action of the ciliary muscle and transfer it with enough force to cause adequate IOL deformation and accommodation.